The anterior pituitary (also called the adenohypophysis, from Greek adeno, "gland"; hypo, "under"; physis, "growth"; hence, glandular undergrowth) comprises the anterior lobe of the pituitary gland and is part of the endocrine system. Unlike the posterior lobe, the anterior lobe is genuinely glandular, hence the root adeno in its name.
Under the influence of the hypothalamus, the anterior pituitary produces and secretes several peptide hormones that regulate many physiological processes including stress, growth, and reproduction.
The term "pars distalis" is sometimes used as a synonym for the anterior pituitary, but this is not quite correct. The anterior pituitary is usually divided into three regions:
pars distalis ("distal part") - the majority of the anterior pituitary
pars tuberalis ("tubular part") - a sheath extending up from the pars distalis and wrapping around the pituitary stalk
pars intermedia ("intermediate part") - sits between the bulk of the anterior pituitary and the posterior pituitary and is often very small in humans
The function of the tuberalis is not well characterized, and most of the rest of this article refers primarily to the distalis.
Embryology
Unlike the posterior pituitary (pars nervosa), which originates from neural ectoderm, the anterior pituitary arises from an invagination of the oral mucosa called Rathke's pouch (which is itself ectoderm derived).
This differentiation is exhibited by the fact that while the posterior pituitary merely secretes those hormones produced in the hypothalamus (ADH and oxytocin), the anterior pituitary actually produces its hormones, while being under control of the hypothalamus as to when they should be secreted.
A useful acronym for the hormones secreted by the anterior pituitary is 'B-FLAT A-PEG' (Basophils release FSH, LH, ACTH, TSH, and Acidophils release Prolactin, Endorphins, GH).
Hypothalamic releasing and release-inhibiting factors
Hormone secretion from the anterior pituitary gland is regulated by hormones secreted by the hypothalamus. Neuroendocrine neurons in the hypothalamus project axons to the median eminence, at the base of the brain. At this site, these neurons can release substances into small blood vessels that travel directly to the anterior pituitary gland (the hypothalamo-hypophysial portal vessels).
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